How to use choiceDispatchKey when the key is a blank character?

[Roger L Costello]

Hi Folks,

I am reading a subsection code (1 character) into this element:

<xs:element name="Subsection_Code" type="xs:string"
                    dfdl:lengthKind="explicit" dfdl:length="1"/>

Some subsection codes are the blank character.

Then I use choiceDispatchKey on that element that holds the subsection code:

<xs:choice dfdl:choiceDispatchKey="{Subsection_Code}">

I get this error message when I run my DFDL schema:

Schema Definition Error: For choiceDispatchKey, the string ( ) must not contain 
any whitespace. Use DFDL Entities for whitespace characters.

Is there a workaround?

/Roger